63880-Ch21 - Insp Principles-3e-S 09-05, 05/06, 06/05/07...

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Insp Principles-3e-S 09-05, 05/06, 06/05/07 Chapter 21 INSPECTION PRINCIPLES AND PRACTICES REVIEW QUESTIONS 21.1 What is inspection? Answer : As defined in the text, inspection is the activity of examining the product, its components, subassemblies, or materials out of which it is made, to determine whether they conform to design specifications. 21.2 Briefly define the two basic types of inspection. Answer : The two basic types of inspection are (1) inspection for variables, in which one or more quality characteristics of interest are measured using an appropriate measuring instrument or sensor; and (2) inspection for attributes, in which the part or product is inspected to determine whether it conforms to the accepted quality standard. Inspection by attributes can also involve counting the number of defects in a product. 21.3 What are the four steps in a typical inspection procedure? Answer : As defined in the text, the four steps are (1) presentation of the item for examination; (2) examination of the item for nonconforming feature(s); (3) deciding whether the item satisfies the defined quality standards; and (4) action, such as accepting or rejecting the item, or sorting the item into the most appropriate quality grade. 21.4 What are the Type I and Type II errors that can occur in inspection? Answer : A Type I error is when an item of good quality is incorrectly classified as being defective. It is a “false alarm.” A Type II error is when an item of poor quality is erroneously classified as being good. It is a “miss.” 21.5 What is quality control testing as distinguished from inspection? Answer : Whereas inspection is used to assess the quality of the product relative to design specifications, testing refers to the assessment of the functional aspects of the product: Does the product operate the way it is supposed to operate? Thus, QC testing is a procedure in which the item being tested (product, subassembly, part, or material) is observed during actual operation or under conditions that might be present during operation. 21.6 What are the Type I and Type II statistical errors that can occur in acceptance sampling? Answer : A Type I error occurs when a batch of product is rejected when in fact it is equal to or better than the acceptable quality level (AQL). The associate probability of a Type I error is called the producer’s risk. A Type II error occurs when a batch of product is accepted when in fact its quality is worse than the lot tolerance percent defective (LTPD). The probability of this error is called the consumer’s risk. 21.7 Describe what an operating characteristic curve is in acceptance sampling. Answer : An operating characteristic curve for a given sampling plan gives the probability of accepting a batch as a function of the possible fraction defect rates that might exist in the batch.
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63880-Ch21 - Insp Principles-3e-S 09-05, 05/06, 06/05/07...

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